A typical scroll compressor includes a compression mechanism and a drive mechanism in a casing. The compression mechanism includes a fixed scroll and an orbiting scroll. These scrolls include opposed end plates and spiral wraps that are integrally formed with the end plates and are engaged with each other.
In the compression mechanism of the scroll compressor, a wrap of the fixed scroll (hereinafter referred to as a fixed-side wrap) and a wrap of the orbiting scroll (hereinafter referred to as an orbiting-side wrap) are engaged with each other, thereby forming a compression chamber between the fixed scroll and the orbiting scroll. The orbiting scroll is coupled to a crankpin of a crank shaft (a driving shaft) of the drive mechanism. Rotation of the crank shaft causes the orbiting scroll to orbit around the fixed scroll, and accordingly, the volume of the compression chamber repeatedly increases and decreases. The compression mechanism sucks refrigerant when the volume of the compression chamber increases, and compresses refrigerant and discharges the compressed refrigerant when the volume of the compression chamber decreases.
On the other hand, some scroll compressors include injection mechanisms for injecting intermediate-pressure refrigerant to compression mechanisms (see, for example Japanese Unexamined Patent Publication No. H11-107945). A compression mechanism described in Patent Document 1 includes an injection port that axially penetrates an end plate of a fixed scroll and is open to an intermediate-pressure position of the compression chamber. The injection port is located at a center of a groove formed between spiral turns of a fixed-side wrap and has a diameter smaller than the thickness of an orbiting-side wrap.
In this configuration, the injection port alternately communicates with a first compression chamber formed between the inner peripheral surface of the fixed-side wrap and the outer peripheral surface of the orbiting-side wrap and a second compression chamber formed between the outer peripheral surface of the fixed-side wrap and the inner peripheral surface of the orbiting-side wrap. Specifically, with orbiting of an orbiting scroll, the orbiting-side wrap reciprocates between the inner peripheral surface and the outer peripheral surface of the fixed-side wrap across the injection port. In this reciprocation, the injection port communicates with the first compression chamber when the orbiting-side wrap is located between the injection port and the outer peripheral surface of the fixed-side wrap, whereas the injection port communicates with the second compression chamber when the orbiting-side wrap is located between the injection port and the inner peripheral surface of the fixed-side wrap.
Other compression mechanisms are configured to increase injection flow rates for higher performance (see, for example, U.S. Pat. No. 6,619,936 and Japanese Unexamined Patent Publication No. S63-243481). In each of the compression mechanisms of U.S. Pat. No. 6,619,936 and Japanese Unexamined Patent Publication No. S63-243481, a fixed scroll has an injection port whose diameter is greater than the tooth thickness of an orbiting-side wrap in order to increase the injection flow rate.